基于倏逝波的锥形光纤马赫-曾德尔湿度传感器

提出了一种基于倏逝波原理的光纤马赫-曾德尔湿度传感器，传感器是在2个单模光纤粗锥的传感臂中心通过绝热火焰熔融拉锥处理而成。光由传感器输入端传入，经过第1个粗锥时，将激发出若干高阶模，各模式光传输经过细锥区进入第2个粗锥时被耦合进入传感器输出端。当外界湿度变化时，细锥区倏逝场随之变化，最终导致透射谱能量变化。通过测量透射谱能量变化，可以实现环境湿度传感测量。实验结果表明，在35%~85%RH的湿度变化范围内，透射谱的能量具有相同变化趋势，处于水蒸气吸收峰附近的干涉谷湿度响应灵敏度可达0.157 dBm/%RH，温度交叉灵敏度仅为0.014 %RH/ ℃。该传感器因其制作简单、灵敏度高，温度交叉敏感小等特点，具有很好的应用前景。

Tapered optical fiber Mach-Zehnder interferometer humidity sensor based on evanescent wave

According to the principle of evanescent wave, a humidity sensor based on optics in-fiber Mach-Zehnder interferometer was proposed by using the standard single mode fiber with two waist-enlarged bitapers, and the center of sensing arm was tapered by adiabatic flam-heated fiber tapering machine. The light propagates from the input end of the sensor, the first bitaper excites a number of higher-order modes, each mode transmits through tapered fiber and into the second bitaper, which can be coupled into the output fiber of the sensor. The change of the humidity can lead to the evanescent field of the tapered fiber changing, eventually causes the energy of the transmission spectrum energy to change. The environment humidity sensing measurement can be realized through measuring the variation of transmission spectrum energy. The experimental results show that within the humidity changing scope of 35%~85%, the energies of the transmission spectra have the same variation trend, a valley of interference spectrum near the water vapor absorption peak has the highest sensitivity of 0.157 dBm/%RH, the temperature cross-sensitivity is as low as 0.014 %RH/ ℃. This humidity sensor is advantaged by easy manufacturing, high sensitivity and immunity of temperature cross-sensitivity, it have a great application prospect.